Deviations in the clotting system may result in thrombosis and haemophilia. Thrombosis results in diseases such as myocardial infarction and attacks and is a complication which frequently occurs in surgery and internal diseases. The formation of thrombin occupies a central role in haemostasis and thrombosis. The most efficient drugs for preventing thrombosis and for the treatment thereof are those agents which have the effect that less thrombin appears in clotting blood. Without going into great detail, it is first necessary to state the outlines of the formation and deactivation of thrombin. When clotting occurs in blood, in plasma which is rich in blood platelets (PRP) or in plasma which contains few blood platelets (LPP) the enzyme prothrombinase is produced therein. This can be produced in various ways, namely by the intrinsic reaction route via activation of the contact factors and factor IX or by the extrinsic reaction route via the activation of factor VII by tissue thromboplastin. Factors VIII and V, which are activated by the first traces of thrombin which appear, are essential cofactors. Factor IXa, together with factor VIIIa and clotting-promoting phospholipids, form a complex which activates factor X. Said factor Xa, together with factor Va and phospholipids, forms prothrombinase, the complex which converts prothrombin (factor II) into thrombin (factor IIa).
Pathology teaches that the deactivation of thrombin is extremely important in preventing thrombosis. No living individuals are known who have less than half the normal amount of ATIII, probably because the absence of it is lethal. People having a hereditary condition which results in them having approximately half the normal amount of ATIII suffer from serious thrombotic disease. To reduce the thrombin, provision can be made for it to be produced to a lesser extent or more slowly by inhibiting the prothrombinase or by reducing the prothrombin concentration in the blood or plasma. This method is used in oral anticlotting, in which the synthesis of plasma proteins in the liver, which are required for the clotting process (the clotting factors) is inhibited by administering vitamin K antagonists. Both prothrombin- and prothrombinase-forming factors are sensitive to vitamin K. The amounts of enzyme and substrate are reduced and the rate of formation of thrombin is reduced. A second way of reducing the amount of thrombin in the blood or plasma is more rapid deactivation of thrombin.
As soon as thrombin appears in the plasma, a number of processes for deactivating it occur, which processes thrombin combines to form inert complexes with its natural inhibitors such as antithrombin III (ATIII), heparin cofactor II (HCII), .alpha..sub.2 -macroglobulin(.alpha..sub.2 -M) and others. Various pharmaceuticals such as, inter alia, the various types of heparin or dermatan sulphate, heparin sulphate, pentosan polysulphate, lactobionic acid or acidic mucopolysaccharides obtained, for example, from Stichopus japonicus (SJAMP) increase the effect of ATIII and/or HCII, which results in more rapid deactivation of thrombin occurring. It is also possible to administer substances which act directly on thrombin without an inhibiting plasma protein also being necessary; such as hirudine (Stone and Hofsteenge, Biochemistry, 25, 4622 (1986)) and synthetic direct thrombin inhibitors such as MD850 (Kumada and Abiko, Throb. Res. 24, 285 (1981)).
The rate of deactivation is proportional to the amount of thrombin present. As long as the rate of thrombin formation exceeds that of the deactivation, the concentration of thrombin in the plasma increases. When the prothrombin is exhausted, the rate of thrombin formation decreases, the deactivation soon acquires the upper hand and ultimately no active thrombin is left (FIG. 1, curve A). The area under the curve indicates how much thrombin has been active in the clotting blood or plasma and for what length of time. This thrombin concentration/time integral is termed the thrombin potential. The potential may decrease (FIG. 1, curve B) if less thrombin is present during coagulation and/or thrombin is present for a shorter time. During treatment with the antithrombotics described above, the thrombin formation curve alters in one or more of the following respects (FIG. 1, curves A and B). It begins later, i.e. the latency time before explosive formation of thrombin occurs is longer, the peak is lower and the decrease is more rapid, with the result that the thrombin present is deactivated earlier. It has been shown that both a reduced formation (in the case of oral anticlotting) and a more rapid decrease (in the case of treatment with heparin) are effective antithrombotic treatments. Both result in a smaller area under the thrombin formation curve. Said area, the time/concentration integral or the endogenous thrombin potential ETP, is therefore capable of being a good measure in determining the effectiveness of treatment with antithrombotics. The present method serves to determine a number (hereinafter to be termed the endogenous thrombin potential ETP) which shows how much thrombin has been active in the clotting blood (blood plasma) and for what length of time.
As far as is known, there is no method of measuring the ETP or a variable quantity of comparable importance. There is a method of calculating the ETP from a thrombin formation curve, which is involved and time-consuming, and there are a plurality of tests for tracking the effect of various types of treatment with antithrombotics with more or less specificity. Said tests are clearly different from, and/or more cumbersome than, the present method and are briefly described below.